The present invention relates to a method for making balloons for catheters used in medical dilatation procedures.
Balloon catheters are being used extensively in procedures related to the treatment of blood vessels. For example, arterial stenosis is commonly treated by angioplasty procedures which involve inserting balloon catheters into specific arteries. Balloon catheters have also been found useful in procedures involving dilation of body cavities.
The most widely used form of angioplasty makes use of a dilatation catheter which has an inflatable balloon at its distal end. Using fluoroscopy, a physician guides the catheter through the vascular system until the balloon is positioned across the stenoses. The balloon is then inflated by supplying liquid under pressure through an inflation lumen to the balloon. The inflation of the balloon causes stretching of a blood vessel and pressing of the lesion into the blood vessel wall to reestablish acceptable blood flow through the blood vessel.
In order to treat very tight stenoses with small openings, there has been a continuing effort to reduce the profile of the catheter so that the catheter can reach and pass through the small opening of the stenoses. There has also been an effort to reduce the profile of the catheter after an initial use and deflation of the balloon to permit passage of the catheter through additional lesions that are to be treated or to allow entry and retreatment of lesions that reclose after initial treatment.
One factor manipulated to reduce the profile of the dilatation catheter is the wall thickness of the balloon material. Balloons for dilatation balloon catheters have been made from a wide variety of polymeric materials. Typically the balloon wall thicknesses have been on the order of 0.0003 to 0.003 inches for most materials. There have been continuing efforts, however, to develop ever thinner walled balloon materials, while still retaining the necessary distensibility and burst pressure rating, so as to permit lower deflated profiles.
The profile of the deflated balloon is limited by the thickness of the waist and cone portions of the balloon. Usually, the waist and cone wall thicknesses are thicker than that of the body of the balloon due to the smaller diameter of the waist and cone portions. In order to reduce the overall profile of the deflated balloon, reduction of the wall thickness of the waist and cone portions must be addressed.
Prior art balloon forming techniques involve stretching and blowing of the balloon from a segment of extruded polymer tubing. Balloons produced by stretching and blowing a tubular preform or "parison" typically have much thicker waist and cone walls than the wall thickness of their body portions. The thicker cone walls contribute to the overall thickness of the catheter, making tracking, crossing and recrossing of lesions more difficult. Further, thick cones interfere with refolding of the balloon on deflation so that the deflated balloon can only be further inserted or withdrawn with difficulty, occasionally even damaging the blood vessel. Thin wall thicknesses enable the deflated balloon to remain narrow, making it easier to advance the balloon through the arterial system.
There have been several solutions proposed for reducing the cone or waist thickness of catheter balloons in U.S. Pat. Nos. 4,906,241, 4,963,313, 5,087,394, 5,304,340, EP 318,919 and EP 485,903. U.S. Pat. Nos. 4,906,241 and 4,963,313, both to Noddin, disclose heating a portion of the balloon preform to a desired temperature and drawing the segment so as to form a necked down region while maintaining a portion of the preform in a crystalline state. The preform may then be blown into a balloon. U.S. Pat. No. 5,304,340 to Downey discloses a method of making a dilatation balloon employing a reverse temperature gradient across the sidewall of a parison and drawing and expanding the parison subject to the temperature gradient.
EP 318,919 to Noddin et al. discloses a procedure in which a portion of the tube is crystallized to render it dimensionally stable under heated conditions. The portion stabilized cannot be appreciably inflated or drawn. The tube is heated in a heated bath and as one end is secured in place the other is drawn to a desired length and in the process is necked-down. The tube is drawn down to a constant diameter sleeve. After the initial necking-down of the tube, the tube is reversed in the bath and the second necked-down portion is formed by the same procedure. After the preform is complete the tube is submerged horizontally and restrained at both ends. Two conical portions at opposing ends are arranged to define the shape of the tapered sections of the balloon. Simultaneously the tube is drawn and expanded without constraint until the molecules of the wall material in the balloon region become stabilized in a biaxially oriented condition. The portions of the tube having the preform tapers expand until they are constrained to the shape of the constraining cones.
U.S. Pat. No. 5,087,394 discloses a method of forming a balloon wherein a length of polymer tubing is formed by drawing the tubing material from an extruder using an extruder die and then irradiated. The method involves positioning an internal support mandrel within the tubing and compressing a portion of the intermediate segment onto the mandrel with a body clamp. The end segment is heated and stretched longitudinally to the desired length. The process of pulling the tube through a restricted hot die or body clamp forms the necked portions and thin waist segments. The other end segment is optionally stretched in a similar manner. The tubing is then heated, and radially stretched by blow-molding to define the balloon and cooled.
EP 485,903 describes a method wherein a tubular parison is formed of a drawable or orientable polymer. It is heated in a metal mold in the range from the second-order transition temperature to the first-order transition temperature of the polymer used. The parison is stretched in the direction of its axis and then inflated radially resulting in a biaxially-drawn or biaxially oriented crude balloon. The parison is then cooled below the second-order transition temperature and deflated. The tapered portions of the crude balloon are redrawn by stretching to reduce their wall thicknesses. The balloon is inflated again and heated above the second transition temperature and then cooled.
The Levy patents (U.S. Pat. No. Re 32,983 and Pat. No. Re 33,561) teach drawing the tubing by axially pulling the tube in a uniform manner apart and then expanding the tube with fluid in a confining apparatus. The stretch process occurs at a temperature above the glass transition temperature and below the melting temperature of the tubing material.
Another method of reducing the cone thickness of balloons is disclosed in U.S. Pat. No. 5,826,588 to Forman, the contents of which are incorporated herein in their entirety by reference. An excimer laser is used to remove portions of the cones from a balloon via photochemical ablation. This materials removal process occurs after the balloon has been formed.
It is possible to make balloons from a variety of materials that are generally of the thermoplastic polymeric type. Such materials may include: polyethylenes, ionomers, ethylene-butylene-styrene block copolymers blended with low molecular weight polystyrene and, optionally, polypropylene, and similar compositions substituting butadiene or isoprene in place of the ethylene and butylene; poly(vinyl chloride); polyurethanes; copolyesters; thermoplastic rubbers; silicone-polycarbonate copolymers; polyamides; and ethylene-vinyl acetate copolymers. Orientable polyesters, especially polyethylene terephthalate (PET), are among the preferred materials for forming catheter balloons.
Other references illustrating the materials and methods of making catheter balloons include: U.S. Pat. Nos. 447,989 and 4,456,000 to Schjeldahl et al, U.S. Pat. No. 4,490,421, U.S. Pat. No. Re 32,983 and Pat. No. Re 33,561 to Levy, and U.S. Pat. Nos. 4,906,244, 5,108,415, 5,156,612 to Pinchuck et al. and U.S. Pat. No. 5,807,520 to Wang et al.
All US patents and applications and all other published documents mentioned anywhere in this application are incorporated herein by reference in their entirety.